It is priorly known to manufacture hollow tubular members (for example, wave guides and cable sheaths) by the steps of continuously drawing a metal strip in a longitudinal direction through a plurality of forming rolls to form a hollow tubular member, and then continuously welding the longitudinal abutting edges of the hollow tubular member. Further, with respect to cable sheath, it is known to form the metal strip around a cable core prior to the step of continuously welding the longitudinal abutting edges of the sheath.
Often wave guides and cable sheaths manufactured in accordance with the priorly known method and apparatus have been found to have deleterious deviations in their thickness along their longitudinal axes. In the main, such deviations were reflections of deviations in thickness of the metal strip employed. Since it was technically impossible to insist upon a supply of metal strip of constant thickness, there was a need for avoiding such deviation reflections.
As to cable sheaths for submarine cables there is a requirement that the cable sheaths have a cross-section of constant area, and that the cable sheath and the cable core be tangentially and longitudinally anchored to each other so as to present an extended unitary structure. Submarine cables referred to herein are of the type that may include a copper sheath, and a cable core comprised of a plurality of electrical and optical conductors having a plurality of steel wires stranded concentrically around them for tension reinforcement.